Method and agent for treating molten iron and steel



Patented Apr. 21, 1942 METHOD AND AGENT FOR TREATIlQG MOLTEN IRON AND STEEL James H. Critchett, Douglaston, and Walter Crafts, Niagara Falls, N. Y., assignors to Eleetro Metallurgical Company, a corporation of West Virginia 7 y No Drawing. Application October 2 1940,

Serial No. 359,343

2 Claims. 1 Cl. 75-58) The invention relates to a method and agent suitable for the treatment of molten iron and steel to promote a fine grain structure and freedom from deleterious impurities. This application is in part a'continuation of our application Serial No. 201,931 (Patent No. 2,221,781), filed April 14, 193B.

During manufacture, steels becomecontaminated with oxides and occluded gases, some of which, if not removed or rendered innocuous, detrimentally affect the soundness and physical properties of the finished steel. To overcome the deleterious effects of such impurities, an addition of ferro-silicon or ferromanganese, or both, as deoxidizers, is usually made to the steel shortly before casting into ingots or other shapes. For further deoxidation, and to provide an inherently fine-grained steel having inhibited grain growth tendencies at elevated temperatures, a later addition of aluminum is often made to the molten steel.

Aluminum additions, in the amounts, for the purposes, and in the manner described above, tend to produce a steel containing deleterious types and quantities of non-metallic inclusions.

It has been proposed to substitute for the aluminum other agents, such as vanadium, or titanium, but none of these elements is entirely satisfactory. Vanadium is usually too expensive to add in an amount sufiicient to produce the desired results, and titanium as heretofore used tends to produce a steel containing numerous objectionable non-metallic impurities.

According to the present invention, a steel that is substantially free from deleterious, gaseous or solid non-metallic impurities and that has improved mechanical properties (including improved impact strength) and excellent fine grain characteristics is produced by adding to the steel while it is molten in the ladle or otherwise shortly before casting, an addition agent containing to 85% (preferably to 55%) of silicon; 3% to 20% aluminum; at least one metal selected from the group consisting of beryllium and boron, in aggregate percentage between 0.1% and 5%; and at least one metal selected from the group consisting of titanium, zirconium, cerium, hafnium, and thorium, in aggregate percentage between 3% and 20%; remainder iron. Iron is present as an impurity or diluent unavoidably introduced in producing an economical and commercially practicable material, and should not exceed about 65%.

The constituents of the addition agent are preferably prealloyed in the form of a master alloy; but they may be unalloyed or only partially alloyed, and used in the form of a briquette of comminuted material. Also, some of the constituents thereof may suitably be in the form of easily reducible or decomposable compounds such as nitrides, nitrates or mixtures thereof. It is essential, however, that the constituents be closely associated.

In practicing the process of the invention, we prefer to add to the molten steel being treated a sufficient amount of the addition agent of the invention that the silicon content of the steel is increased by about 0.25%. The deoxidizing or grain refining power may be controlled and varied by adding more or less than enough material to increase the silicon content of the steels by about 0.25%, or alternativeLv, the concentration of silicon relative to the other constituents of the addition agent may be varied. If less grain refinement is required, part of the silicon required for deoxidizing may be added as the agent of the invention and part as ordinary ferrosilicon, and if more grain refinement is required, the action of the addition agent may be supplemented by an addition of aluminum or other grain refiner.

The desired composition may be added to the steel in any well known manner, for example, in the furnace, in the ladle, or in the molten stream during pouring. When adding the addition agent to the steel either in the ladle or in'the molten stream, an agent containing less than about 50% iron should ordinarily be used in order to minimize the chilling effect of the iron. If the agent is added to the steel in the furnace, the iron content of the agent may be greater than 50%.

By proper selection of elements, a grain size of No. 6 or No. 7 may readily be procured in steels treated according to a method of the invention. Throughout the present specification, grain size refers to austenitic or inherent grain size determined by the McQuaid-Ehn carburizing test conducted at a temperature of 925 C. for 8 hours, as defined by the A. S. T. M. specification E 19-33. The degree of grain refinement or deoxidation of the steel per unit of addition agent added will vary, not only with the combination of elements selected, but also with the type of steel being treated, so that the total amount of agent to be added to the steel for best results must be determined by trial. Ordinarily, this total amount of agent will be less than 5%, and most frequently less than 1%.

While the. addition agents of this invention are especially useful in the treatment of steels which are to be hot worked, the invention is also applicable to the treatment oi steels which are to be employed as castings. Used for the latter purpose, it has been iound that, in many instances, the characteristics oi the casting may be improved if the material of the invention is added in an amount which is sumcient tonde-i oxidize the metal, yet is insumcient to develop harmful inclusions.

Steels treated according to the invention are sound, substantially free irom'excessivenommetallic inclusions, and-possess improved ductil-. I ity and shock resistance. Further, the i'ew inclusions distributed throughout such steels are more uniiorm than diverse, that is, are not segre;

gated. Theidegree of grain refinement that can be produced without the formation or harmful inclusions is greater than that attainable bi ths addition of aluminum alone.

1. A composition oi matter, suitable for use as an addition agent for treating molten ferrous metal, consisting substantially of 25% to-'-85% tim silicon; iron, 8% to 20% aluminum; at least one element selected from the group consisting of beryllium and boron, in an aggregate percentage between 0.1% and 5%, and at least one metal of the group consisting of titanium, zirconium, cerium, hafnium, and thorium, the total percentage oi the element or elements from the latter .group being between 3% and 20%.

2. A method of treating molten ferrous metal "which comprises adding thereto a small but efiective' amount of an addition agent con is of 125% to 85% silicomiron; 3% to 20% aluminum; at least one element selected from the group consistingoi beryllium and boron, in an aggregate percentage between 0.1 and 5%; and at least one-element selected from the group consisting ot'fftitaitiium, zirconium, cerium, hafnium, and

thorium, the total percentage of the element or elements of the latter group being between 3% and 20%.

JAMES H. WALTER cams. 

